This invention generally relates to vault systems for the below ground disposal of hazardous waste, and is specifically concerned with a side loading vault system and method for the disposal of low-level radioactive waste.
Burial systems for the disposal of radioactive and other types of hazardous waste are known in the prior art. In some of these systems, a large hole is excavated in the earth, and a floor structure formed from a concrete slab and a layer of gravel is constructed therein. Radioactive waste that has been packaged in 55 gallon steel drums is then stacked over the floor structure of the burial site. In some of these systems, monitoring equipment in the form of drain pipes is laid around the floor structure so that leakages of radioactive wastes through the 55 gallon steel drums may be detected before the waste has an opportunity to contaminate ground water. After the burial site has been completely filled with radioactive waste, water impermeable layers of plastic material and compacted clay are placed over the waste, followed by an earth cap onto which erosion-resistant vegetation is often planted. In some burial type systems, a layer of concrete is poured over the waste prior to overlaying it with compacted clay and an earth cap.
Unfortunately, there are a number of shortcomings associated with such prior art burial-type systems that significantly limit their ability to provide safe and inexpensive storage for hazardous waste. One major shortcoming of such a system is its inability to provide an inexpensive and convenient means of retrieving leaking waste containers. Thus, if the monitoring equipment that is built into these systems should ever indicate the presence of a serious radioactive leak from the containers disposed therein, a large portion of the earth cap, compacted clay, water impermeable plastic and concrete overlying the waste containers would have to be removed, and the leaking containers painstakingly located by lifting the containers out of the burial cavity one-by-one. After the leaking container or containers were finally located, the disassembled portion of the site would, of course, have to be completely reconstructed. Still another shortcoming associated with such prior art burial site designs is the fact that the open burial cavity exposes the waste to rain and other ambient weather conditions during the loading operation. Since it may take as long as four to six months for a utility to completely fill such a burial site with waste, a considerable amount of rain water can accumulate over the floor slab of such a site. While this rain water can be periodically pumped out, the expense associated with such an effort is significant. Moreover, the presence of any standing water in such a site for any length of time promotes the occurrence of corrosion and leaching through the walls of the waste containers in contact with such water. Still another shortcoming associated with such prior art burial sites is the amount of radiation that the system workers receive when loading such a site. The geometry of a top-loaded burial site is such that a worker standing near the rim is exposed to radiation from most every radiation container. Even when the waste deposited in such burial sites is rated as low-level radioactive waste, the effects of such radiation exposure are, unfortunately, cumulative. In addition to radiation hazards, the craning-in of waste packages into a top-loaded burial site makes possible the occurrence of a waste-dropping accident, which could rupture or otherwise damage one or more of the waste containers within the burial site. Finally, because the ceilings of such burial sites depend upon the waste itself for structural support, there is no way that the system operators may reliably inspect the ceilings of such sites for structural faults prior to loading of the waste therein.
Vault-type systems for the storage of such radioactive wastes are also known in the prior art. While such vault-type systems can overcome some of the disadvantages associated with burial-type systems such as the exposure of the waste to ambient weather conditions, none of these systems of which the applicants are aware affords the system operators a convenient and expeditious way of retrieving a leaking waste container in the event that the monitoring equipment indicates the existence of a hazardous leak condition. Moreover, large unitary vault systems formed from brittle construction materials such as concrete are susceptible to cracking in the event of subsidence or a seismic disturbance.
Clearly, there is a need for a vault-type system and method for the disposal of radioactive waste that affords convenient and expeditious access to the contents of the vault in the event that the radiation monitoring system indicates that a dangerous leak condition has arisen. Ideally, such a vault system should shelter the waste from the ambient weather during the loading operation and expose the system operators to only a minimal amount of radiation. The vault system should have the capacity to store large volumes of radioactive waste but yet not be susceptible to cracking in the event of subsidence or seismic disturbances. Finally, the vault system should be amenable to inspection prior to the loading of waste packages therein, and should not set the stage for the occurrence of dropping accidents which could rupture or otherwise damage waste containers during the loading operation.